Circulating monocytes are obtained from normal and obese patients. The monocytes have been shown to have receptors for insulin. Using the radio-receptor assay techniques to demonstrate binding of insulin to the patients' receptors it has been found that obese patients have a decrease in receptor concentration. Chronic dieting in the obese patients causes an increase in receptor concentration. In the basal, fed state and chronic diet, total receptor concentration was inversely related to the patient's circulating plasma insulin level. A 72 hour fast resulted in an increase of receptor concentration only at low concentration of insulin; this binding increase is associated with a change in receptor affinity. These studies are to be extended to other disease states in humans.